Spark plug shield



y 1943- E. N. JACOB] 2,323,399

SPARK PLUG SHIELD Filed Nov. 15, 1941 C onduct/ng Rubber 2940M Edward MJambz Patented July 6, 1943 SPARK PLUG SHIELD Edward N. Jacobi,Milwaukee, Wis., assignor to Briggs & Stratton Corporation, Milwaukee,Wis., a corporation of Delaware Application November 15, 1941, SerialNo. 419,250

10 Claims.

This invention relates to shields for electrical appliances, and refersparticularly to electrostatic and electromagnetic shields for sparkplugs.

As is well known to those skilled in the art. it is desirable to shieldthe spark plugs of internal combustion engines to prevent their causinginterference to radio reception. Heretofore these shields have been madeof metal. An illustration of the type of shield in common use may befound in Patent No. 2,151,112 issued to Edward N. Jacobi, March 21,1939.

Such metal shields are expensive to manufacture and difllcult to apply.It is, therefore, an object of this invention to provide a simplifiedspark plug shield capable of being quickly and easily applied.

Another object of this invention is to provide a shield of the characterdescribed which although composed entirely of rubber, has electrostaticand electromagnetic shielding qualities.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts subs an ia y as hereinafterdescribed and more particularly defined by the appended calims, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaims.

The accompanying drawing illustrates one complete example of thephysical embodiment of the invention constructed according to the bestmode so far devised for the practical application of the principlesthereof, and in which:

Figure 1 is a cross sectional view through a shield embodying thisinvention, illustrating the same applied to a spark plug;

Figure 2 is an end view thereof; and

Figure 3 is a bottom view thereof.

Referring now particularly to the accompanying drawing in which likenumerals indicate like parts, the numeral 5 designates generally ahoodlike enclosure adapted to be applied to a spark plug 6 and toaccommodate the shielded lead I which is connected to the terminal 8 ofthe plug.

The hood-like enclosure 5 has a. laminated wall the inner layer 9 ofwhich is formed of ordinary soft insulating rubber while the outer layerIll thereof is formed of a rubber material recently developed and knownto the trade as conducting rubber."

Such "conducting rubber" is described in India Rubber World 100:6, page38, September 1939; and in Rubber Ag 47, page 308, August 1940. Asdescribed in these articles conducting rubber can be made with aresistance as low as 1 ohm per cubic centimeter of rubber. As will beapparent conducting rubber of low resistance is most desirable for theattainment of good electrostatic shielding qualities.

This material has all the characteristics of ordinary rubber except thatit is impregnated with a metallic substance to render the sameelectrically conductive.

The two laminations are vulcanized or otherwise secured together and toinsure an electrical grounding connection between the outer laminationof conducting rubber with the metal base of the plug and the metalcovering of the shielded lead, the outer lamination is turned in overthe openings in the enclosure through which the plug and lead pass.

Thus the inturned portion ll of conducting rubber which bounds the edgeor the opening I2 through which the plug passes, snugly engages the nutof the sp rk plug base, while the inturned portion l3 which bounds theopening H through which the lead passes firmly rips he me l sheath ofthe shielded lead 1.

Being formed of rubber as it is, the hood-like enclosure is readilypulled onto the spark plug and fitted to the shielded lead, and as willbe readily apparent to those skilled in the art, the shield thus formednot only serves as an effective electrostatic and electromagneticbarrier to preclude radio interference, but also serves to protect theplug from the elements.

What I claim as my invention is:

1. An electrostatic shield for electrical appliances such as spark plugscomprising: a hood adapted to fit over the appliance and formedessentially of rubber with the outer layer thereof composed ofconducting rubber and the inner surface electrically insulating.

2. A shield for spark plugs and the like comprising: a hood formed ofrubber and of a size to fit over a spark plug and the adjacent endportion of its lead, the inner surface of said hood being electricallynonconducting, and at least the outer surface of the hood havingelectrical conducting characteristics.

3. A shield for spark plugs and the like comprising: a hood shaped tofit over the plug and over the adjacent end portion of its lead, saidhood being formed essentially of rubber and having a laminated wall, theinner lamination of which is a good insulator, and the outer laminationof which is of conducting rubber.

4. A shield for spark plugs and the like comprising: a hood shaped tofit over the plug and over the adjacent end portion of its lead, saidhood being formed essentially of rubber and having a laminated wall, theinner lamination of which is a good insulator, and the outer laminationof which is of conducting rubber, said outer lamination extending aroundthe edges or the openings in the hood through which the spark plug andits lead pass so as to have electrical contact with the metal portionsor the spark plug base and the external covering of the lead.

5. An electrostatic shield for electrical appliances such as spark plugscomprising: a hollow body adapted to fit over the appliance, said bodyhaving openings through which metallic parts of the appliance enter theinterior of the body; and elastic portions on the body bounding saidopenlugs and 01' a size to snugly grip the metallic parts receivedtherein and thereby securely position the shield on the appliance, saidbody and its elastic portions having a continuous electrical conductinglayer which is exposed at the insides oi said elastic portions to haveelectrical contact with the metal parts gripped thereby.

6. A shield for spark plugs and the like comprising: a one-piece rubberhood of a size to fit over a spark plug and the adjacent end portion ofits lead, said rubber hood comprising a continuous layer of conductingrubber adapted to enclose the spark plug and having elastic portionsformed to resiliently grip the metal portions of the spark plug base andthe external covering of the lead so as to electrically connect saidportions or the base and lead.

7. A shield for spark plugs and the like comprising: a one-piece rubberhood of a size to fit over a spark plug and the adjacent end portion ofits lead, said rubber hood comprising a continu ous layer of conductingrubber adapted to enclose the spark plug and having elastic portionsformed to resiliently grip the metal portions or the spark plug base andthe external covering 0! the lead so as to electrically connect saidportions or the base and lead; and means for electrically insulating thelive parts or the plug and its lead from the conducting surfaces of thehood.

8. A shield for spark plugs and the like comprising: a hood formed ofrubber and shaped to fit over the plug and over the adjacent end portionof its lead, said hood having elastic portions for yieldingly grippingthe metal portions of the spark plug base and the external covering ofthe lead; and conducting surfaces at the exterior oi the hood andsurrounding the plug and the adjacent end oi! its lead; said conductingsurfaces extending into the elastic gripping portions of the hood to beheld in good electrical contact with the metal portions or the plug baseand lead covering by the elasticity of said elastic portions.

9. A- shield for spark plugs and the like comprising: a hood havingelastic electrical conducting portions for gripping the metal parts ofthe spark plug base and the covering for its lead; and a body Joiningthe elastic portions and having an electrically conductive layer forenclosing the plug and for electrically connecting said elasticportions.

10. .A shield for spark plugs and the like comprising: a hood havingelastic electrical conducting portions for gripping the metal parts ofthe spark plug base and the covering for its lead a body joining theelastic portions and having an electrically conductive layer forenclosing the plug and for electrically connecting said elasticportions; and a lining of non-conducting material on the interior of thebody at least at the region 01 the spark plug terminal.

EDWARD N. JACOBI.

